Peter and Mary were in her backyard on a sultry summer evening, racing after fireflies.
“Hey! I caught one!” Mary shouted with happiness.
“Ooh! Pretty!” said Peter.
“Not your firefly; look up there!”
Following Peter’s outstretched arm, Mary looked up just in time to see the end of a meteor as it blazed across the sky.
“I wonder what makes them glow like that,” she mused. “Do you think that they are radioactive?”
“No; it is probably sunlight reflecting off of them like those noctilucent clouds that Mr. Medes told us about in science class last year.”
“Well, it is nice to know that you paid attention to something that I said,” came a voice from behind them.
“Mr. Medes!” the pair exclaimed.
“What are you doing here?” continued Mary.
“Your mother asked me over to see her new telescope,” he replied. “But it looks as if we won’t need it to see the meteor shower.”
“That’s right; they move too quickly to see in the telescope. But what makes them glow like that?” asked Peter.
“That’s an interesting question,” Mr. Medes said. “To answer it, you’ll need to rub your hands together. What do you think will happen?”
“They’ll make noise,” Mary said promptly.
“They’ll get hot,” said Peter.
“OK, you’ve made your predictions – now find out what the answer is!” commanded Mr. Medes.
Eagerly, the pair began to rub their hands vigorously together.
“Hey! My hands are getting warm!” said Mary.
“We learned about this in Boy Scouts,” said Peter. “When you rub things together, the friction between them makes heat. You can even use it to make fire by rubbing sticks together!”
“That’s right,” said Mr. Medes. “When you rub things together, you are taking one type of energy and turning it into another. You are taking energy of motion”
“Kinetic energy!” interjected Mary.
“That’s right; you are turning kinetic energy into heat energy. You can do the same thing by hitting a piece of metal with a hammer. Do it fast enough and you’ll heat the metal up so much that it glows!”
“But what does that have to do with meteors?” asked Peter.
“Well,” Mr. Medes said, “People used to think that it was the friction of the meteorite racing through the air that made them glow. And it does have some effect; some of the little bits that break off are torn away by friction. But there’s something else that has an even bigger effect. To understand it, you’ll need a basketball and an air pump.”
“I’ve got those in my garage!” Peter exclaimed. He quickly raced next door to get the equipment and handed it to Mr. Medes when he got back.
“Wow! That was quick! You almost started to glow yourself,” Mr. Medes joked. Taking the air pump,he plugged it into the basketball. “I want you both to feel the basketball. Tell me, does it feel warmer or cooler than the air around it?”
Looking puzzled, Peter and Mary put their hands on the basketball.
“They feel about the same,” Mary said.
“Yeah, it feels like everything else out here,” Peter added.
Mr. Medes nodded. “That’s because the air and the basketball are in what scientists call ‘thermal equilibrium’; the ball gains heat from the air about as quickly as it gives heat back. Now what I want you to do is take turns pumping air into the basketball. You’ll need to add fifty pumps each. What do you think will happen?”
“The ball can’t get much bigger,” Peter said. “It is already full of air. So it will be just the same.”
“I don’t know,” Mary replied. “If we are adding more air to the ball, then something has to happen. Maybe it will change temperature?”
“There’s only one way to find out,” Mr. Medes said. “Start pumping!”
What do you think will happen? Do the experiment!
“Ladies first!” Peter said, handing the pump handle to Mary. She started eagerly enough, but soon was huffing and puffing each time she pushed the air pump’s handle down.
“Gosh, this is hard!” Mary said. Finally, she finished her fifty pumps. “Your turn!”
“Stand back and watch what a boy can do!” Peter said. His first few attempts went smoothly enough, but pretty soon he was as out of breath as Mary had been. “Maybe I spoke too soon!”
As soon as Peter had finished adding the air to the basketball, Mr. Medes picked it up and said “look at the ball. Is it any bigger?”
When the two shook their heads “no”, he continued “But add all of that air had to do something. Touch the basketball and let me know what you feel.”
Peter and Mary put their hands on the basketball. After a moment, Peter’s face lit up with understanding.
“The ball is warmer than it was!” he exclaimed. “Adding all of that air made it warmer somehow!”
“That’s right,” Mr. Medes said. “When you added the air, you compressed a lot of stuff into a small space. That meant that the stuff couldn’t move as far without running into something, so it started moving in shorter but faster ways. And that means…”
“That the temperature went up!” Mary exclaimed. “Because temperature is just the motion of the molecules; the faster they move, the hotter they are!”
“That’s close enough for now,” Mr. Medes said. “There are a few differences between temperature and heat, but those only matter to a scientist. Your idea is right, and that’s the important thing. When you compress air, it heats up. And that explains the meteor’s glow.”
“How?” Peter asked. “I still don’t get the connection.”
“Those meteors that you see in the sky are little tiny grains of dust that are moving very, very fast. The slowest of them are moving at 24,000 miles per hour and the fastest are trucking along at 94,000 miles per hour. That is so fast that the air can’t get out of the way as the meteor heads toward Earth. So when the dust grain enters the atmosphere, it compresses the air in front of it.” Mr. Medes pushed one hand with the other to show what he meant. “The air transfers some of that heat to the meteor and that heats up the meteor until it glows. Sometimes the outer skin of the bigger ones melt and little drops fly off as it goes through the atmosphere,”
“Is that what makes the little trails that come off of the meteor as it goes through the sky?” asked Peter.
“Yes. Sometimes the meteor hits the air so hard that it is blasted apart, like the one in Russia. And sometimes the meteor is so big that it makes it all the way to the ground,” Mr. Medes continued. “That makes a crater that we call an astrobleme, or ‘star wound’. You’ve probably heard about the one that hit about 65 million years ago.”
“That’s the one that killed the dinosaurs!” Mary said.
“Well, let’s just say that Chicxulub didn’t do them any favors,” chuckled Mr. Medes. “And it isn’t the only one. There are literally hundreds of astroblemes on Earth, and even more on the Moon. And now that your mother has her telescope set up, let’s take a look at those.”
Smiling, the three turned to look through the telescope at the face of the Moon.